Amino-triazolinone of the present invention is synthesized by using hydrazine as a starting raw material and adding phosgene which is a poisonous gas in the middle as shown in the following Reaction Formula. The above-described process, which is the first developed process by Bayer AG in Germany, finally produces amicarbazone which is a prominent plant growth regulator. The amicarbazone is mainly used in a large farm producing sugar canes and cones, and in accordance with an increased demand for the sugar cane which is a raw material for preparing bioethanol and a raw material of raw sugar, a demand for an herbicide has also become increased.

Since the amino-triazolinone of the present invention was known in a prior document (see J. Heterocyclic Chem., 21(6), 1769˜74 (1984)), methods of preparing the same have been registered as a patent; however, these patents are mostly directed to a method for preparing amino-triazolinone using phosgene. Representative inventions using phosgene have been disclosed in U.S. Pat. No. 4,952,701 (filed in 1988), U.S. Pat. No. 5,693,821 (filed in 1996) and U.S. Pat. No. 5,912,354 (filed in 1998) in detail (see the known patent documents for details).